Picture reproducing system



Filed March 23, 1932 DIRECTION BRIGHTNESS WIDTH OF SCANNING SPOTADDITION YIELDS CONSTANT AVERAGE BRIGHTNESS |NVENTOR FRITZ SCHROTERATTORNEY Patented Oct. 27, 1936 UNITED STATES PATENT OFFICE PICTUREREPRODUCING SYSTEM Germany Application March 23,

1932, Serial No. 600,698

In Germany March 14, 1931 2 Claims.

As an auxiliary means in the amplification of picture-point currents inpicture telegraphy and in television, there is mostly used an auxiliarycarrier wave of a frequency being higher than the highest pictureimpulse frequency to be amplified. This auxiliary carrier wave issupplied at the lowest possible point of the amplifier arrangement, say,by the periodic interruption of the light ray pencil scanning thepicture to be transmitted by the aid of a revolving perforated wheel. Atthe receiving end the said carrier frequency can be eliminated again bythe aid of rectification in conjunction with selective means in orderthat the means serving for the recreation of the picture(electrochemical recording device, glow-discharge lamp, Kerr cell,string galvanometer, etc.) will be acted upon only by the picturesignals. However, in many instances elimination of the carrier frequencyat the receiver end is dispensed with in order that the device recordingor re-creating the picture may be adaptable to the end or power stage ofthe amplifier; in fact, some picture re-creators such as agaseous-conduction lamp with external electrodes, as a matter ofprinciple, are operable only by the aid of modulated carrierfrequencies. In cases of this kind the carrier frequency must be chosenvery high in order that the same will not be analyzed by (or act upon)the picture scanner means, and that no disturbing screens may arise inthe incoming re-created picture. On the other hand, however, very highcarrier frequencies are attended with serious drawbacks inasmuch as inthe case of transmission over wire circuits (cables) these are usuallynot designed therefor, while in the case of radio transmission, thereresult inadmissibly wide side-bands.

Before describing the invention in detail, attention is directed to thedrawing in which Fig. 1

shows one embodiment of the invention, and Fig. 2 shows a schematicdiagram for illustrating the theory underlying the invention.

The invention discloses ways and means adapted to preclude theproduction of a disturbing screen impression in the incoming orre-created picture by the aid of comparatively low carrier frequencies.The basic principle of the invention shall be explained more fully byreference to a television receiver the essential parts of which areillustrated in Fig. 1. Referring to the latter, I denotes part of theNipkow disk serving as a picture point distributer, 2 is the picturewindow, and 3 the glow discharge or gaseous conduction lamp to which theincoming currents are fed. The running coordinate of the middle of thescanning slit which, for instance, is constituted by a quadratic hole,shall be taken to be in the rectilinear line direction 9:, and the widthof the scanner disk in its direction of motion shall be supposed to beI. If, then, the glow discharge lamp is fed with a sinuous alternatingcurrent potential of frequency 8, the distribution of brightness alongthe picture line upon viewing through the Nipkow disk will be accordingto this relation:

H,=const.[l+ sin z (See Fritz Schriiter, Re-creation and amplificationin televisors Elektrische Nachrichtentechnik, 1929, Vol. 6, page 445,Equation (4) It can be seen from the formula that HX throughout thelength of the lines becomes constant no matter What the value of s, forwhich there holds true this equation:

8=f, f/ f/3, t

Hence, if the auxiliary carrier frequency be chosen in accordance withthis instruction and rule, then, in line with what is desired, the samewill remain invisible in the re-created picture; and it is this fact inwhich the idea underlying this invention resides.

The production of the effect as here dealt with is illustrated also bygraphic means (Fig. 2) which is based upon the case where s=f; in otherwords, during the shifting of the scanning slit by an amount equal toits own width, there occurs exactly a light and dark sequence of thereceiver light source. In the figure the scanner slit in the receiver isshown in nine sequential positions dilfering each one-quarter period(numbers 1-9) the more or less marked darkening of the square slit beingintended to indicate the luminous values resulting from the brightnesscurve shown on the left hand side and corresponding to each case. Byintegration of the brightness values in vertical direction it will beeasy to understand that the sum total in visual observation according tothe Talbot law or the exposure or blackening in photographic recordingor impression in accordance to the law of additions, everywhere resultsin a constant grey which in the case here shown comprises one portionwhite and two portions half-tone.

It can be easily seen that the principle hereinbefore disclosed for theselection of the carrier frequency will be successful in use and in asimilar way in connection with picture telegraphs and televisionreceivers of any desired kind of picture re-creation or re-assembly.

Having now described. my invention, what I claim and desired to secureby Letters Patent is the following:

1. In a system of picture reception wherein the picture field is scannedby an aperture of ,elementary width and varying illumination, the methodof excluding the efiect on the picture of a constant frequency componentof said varying illumination which comprises traversing the apertureacross the field at a speed such that the aperture moves substantiallythe amount of its own width in an integral number of cycles of the saidconstant component.

2. In a system of picture reception wherein the picture field is scannedby an aperture of elementary width and Varying illumination, the methodof excluding the effect on the picture of a carrier frequency intermixedwith the picture impulses which comprises varying the illumination ofthe aperture in accordance with the mixed frequencies, and traversingthe aperture across the field at a speed such that the aperture moves bysubstantially the amount of its own width in an integral number ofcycles of the carrier frequency.

FRITZ SCHROTER.

